The present invention relates to a mooring device comprising a vessel, a body carrying anchor lines which extend in different directions according to catenary lines towards bottom anchors, said body being rotatably supported about a substantially vertical axis by a part which is movably connected with the vessel and held in an initial position with respect to the vessel by means which can give way to allow movement of the vessel away from the said body in case the tension in at least one of the anchor lines exceeds a predetermined value.
A mooring device of this type has been disclosed by the published Dutch patent application 8402398. According to said prior art the rotatable body carrying the anchor lines is rotatably supported at the lower end of a turret which at the top of the bow of the vessel is swingably mounted about a horizontal axis to rigid arms which extend forwardly from the bow of the vessel.
The lower end of said turret is held in abutment against e.g. a bulb extension of the bow of the vessel by means of a weight which keeps the turret against said abutment with a certain predetermined load.
The design is such that under normal weather conditions the vessel may swing around the vertical axis of the turret and can swing around said vertical axis and be displaced by wind, waves and/or currents.
The catenary lines function like a spring the rigidity of which increases rapidly with excursion of the vessel away from its initial position in which it is held by the catenary lines. Under normal weather conditions the load excursion relation remains sufficiently elastic, but under heavy weather conditions, such as heavy storms, the load on the anchor lines, at least on one of said lines, increases to a value which may damage the line or damage parts of the mooring device.
This is particularly the case if stormy weather conditions occur which statistically occur only once in a century. If this occurs said prior art mooring device allows further excursion of the vessel without substantial increase of the load on one or more of the anchor lines because then the load is overcome which keeps the turret against its position allowing the turret to swing about the horizontal transverse axis at the top of the turret. Further excursion of the vessel then is possible without increasing the load until after a certain displacement the anchor lines again become further tensioned.
Swinging about a horizontal transverse axis however means that the initially vertical axis of rotation of the body moves into an inclined position. This has as a consequence that the rotatable body moves into an inclined position as well with its plane of points of connection of the anchor lines. This may lead to rotational swinging movements of said body because if one anchor line is tightened the line extending in the opposite direction is slackened, accordingly has a considerably lower tension so that the tensioned anchor line on the other side might try to move downwardly, thereby rotating the body and lifting the slackened tension line. All this is promoted by the fact that the inclined position of the turret occurs under extremely heavy weather conditions during which the vessel is also rolling about its longitudinal axis and pitching about its transverse axis. Said last mentioned movements lead to swinging of the turret which increases the load on the anchor lines in an uncontrollable way and interferes with the rolling movements about the longitudinal axis of the vessel. The result is heavy loads in the bearings of the horizontal transverse axis at the top of the turret and heavy loads in the entire construction in particular the arms carrying the weight.
Through the turret extends a product line which at least below the rotatable body carrying the anchor lines is a hose. The inclined position of the turret under extremely heavy weather conditions and the swinging of said turret, as described above, may damage the hose with the effect that the environment will become polluted.